DESCRIPTION: The goal of this study is to describe the frequency and type of mutations and polymorphisms in two autosomal dominant, highly penetrant breast cancer genes in cases and controls from a population-based series of Chinese women with breast cancer, unselected for family history. Mutations in the BRCA1 and BRCA2 genes have all been associated with breast cancer in high risk families, that include multiple cases of apparently inherited disease, often at a young age. The majority of these data derive from studies of a small number of high risk Caucasian families with unusually high frequencies of early onset breast cancer. No information is available regarding the frequency, type or presence of founder mutations in non-Caucasian populations, specifically among Asians. As a result, no information is currently available for genetic testing or screening for either Chinese women or Western women living in North America or Europe, who are of Chinese descent. This study seeks to provide and disseminate that information by: 1) determining the frequency and types of mutations in the BRCA1 genes in cases and controls from a large, population-based, case-control study of breast cancer in Shanghai; 2) developing a public data base to distribute the above information, along with information regarding the type and frequency of polymorphisms and rare sequence variants' and 3) comparing the frequency and type of mutations with suspected risk factors for breast cancer. The proposed study will be nested within a randomized, controlled trial, the Shanghai Breast Self-Examination (BSE) Trial, of 267,000 women, designed to examine the effect of breast self-examination on breast cancer mortality in Shanghai, China. Extensive epidemiologic data are already available on this cohort, which may be combined with the proposed molecular study for additional analyses. Information from the above studies could be used to formulate public health policy and diagnostic breast cancer screening strategies on subsets of Asian women, in the future.